Electron tube analyzer



Sept. 8, 1959 H. DoBRovoLNY ELECTRQN TUBE ANALYZER 13 Sheets-Sheet 1 Filed June l, 1956 INVENTOR Sept. 8, 1959 H. DoBRovoLNY 2,903,643

ELEcTRoN TUBE: ANALYZER 15 Sheets-Sheet 2 Filed June l, 1956 INVENTOR Hen/y omuo//y/ m@ 7M M )154,2 Arron/y 13 Sheets-Sheet I5 Filed June 1, 1956 QS 5&5@ Qu Enron/5y Sept. 8, 1959 H. DoBRovoLNY ELEcTRoN TUBE ANALYZER 13 Sheets-Sheet 4 Filed June l, 1956 N www Heng ob/"o a/o/ BY M @emma 5E m Sept` 8, 1959 H. DoBRovoLNY v 2,903,643

' ELECTRON TUBE ANALYZER Filed June 1, 1956 13 Sheets-Sheet 5 QQ J lo |o INVENTOR Sept. 8, 1959 Filed June 1, V195s H` DOBROVOLNY ELECTRON TUBE ANALYZER 13 Sheets-Sheet 6 Fg 4A TUBE UNDER (fao-500MG) INVENTOR BY Mw Sept. 8, 1959 H. DOBROVQLNY 2,903,643

ELECTRON TUBE ANALYZER Filed June l, 1956 13 Sheets-Sheet 'T 7055 UNDER T657 SePt- 8, 1959 H. DoBRovoLNY 2,903,643

ELECTRON TUBE ANALYZER Filed June 1, 1956 13 Sheets-Sheet 9 Sept. 8, 1959 H. DoBRovoLNY ELECTRON TUBE ANALYZER 13 Sheets-Sheet 10 www-{l- Fled June l, 1956 NDW mlm@

Sept. 8, 1959 H. DoBRovoLNY 2,903,643

' ELECTRON TUBE ANALYZER M4575? CONTROL L58 /N P05/770A! 7 Sept. 8, 1959 Filed June 1, 1956 13 Sheets-Sheet 12 INVENTQR Sept. 8, 1959 H. DoBRovoLNY ELECTRON TUBE ANALYZER 13 Sheets-Sheet l5 Filed June l, 1956 SN www Sw@ N Qx nited States Patent ffice 2,903,643 Patented Sept. 8, 1959 ELECTRON TUBE ANALYZER Henry Dobrovolny, Kensington, Md.

Application June 1, A1956, Serial No. 588,933

- 13 claims. (ci. 324-23) (Granted under Title 3S, U.S. Code (1952), sec. 266) The invention described herein may bemanufactured and used by or for the Government of the United States for governmental purposes without the payment tome of any royalty thereon, in accordance with the provisions of 35, United States Code (1952), Section `2.66. t

This invention relates to multipurpose tube analyzers and is particularly directed to an improved tube analyzing apparatus and method capable of measuring and testing the fundamental characteristics of electron tubes with a precision suciently accurate to predict their behavior under actual operating conditions.

Commonly available typesV of portable tube testers which are designed from the standpoint of light Weight, low cost, and ease of operation often fail to indicate the true condition of electron tubes. On the other hand, the operating complexity, size, weight, and cost of laboratory type instruments have prohibited their use in connection with the maintenance of electronic equipment.

1t is accordingly an immediate object of this invention to provide, in a portable and relatively inexpensive tube analyzer, means for testing the true characteristics and serviceability of electron tubes in a manner that will demonstrate their behavior in actualoperating conditions.

It is one object of this invention to provide a tube analyzer in which the various characteristics pertaining to tube quality such' as leakage, transconductance, emission, etc., can readily be measured by the operation of a relatively few, adjustable controls.

A further object of this invention is to provide a multipurpose tube analyzer which will accurately measure characteristics of all commercially available receiving and small transmitting type tubes, the necessary different test circuits being established by manipulation of la few controls. i

Still another object of this invention is the provision in a multipurpose tube analyzer of an improved leakage test circuit which enables leakage current measurements consecutively between each electrode and all other electrodes including shielding electrodes in a tube, the leakage being measured under any selected voltage conditions.

A further object of this invention is to` provide a tube analyzer which enables' quantitative measurements of true grid-plate transconductance (mutual conductance' or Gm) under conditions tailored for each particular tube type.

A still further object of this invention is to provide a tube analyzer which enables determination of tube emissivity under dynamic conditions of tube operation.

In connection with lthe various objectives of this invention there is also yprovide in the apparatus of the present invention, readily accessible connectors which enable the test circuits established in the various test procedures to be employed in connection with testing and analyzing of other types of electronic equipment.

Still another object of this invention is to provide in a multipurpose tube analyzer a Vernier type of indicating` meter control whereby accuracy and sensitivity of meas'- urements is preserved through all selective ranges' at which measurements are made.

A final objective of this invention is to` provide in a multi-purpose tube analyzer an improved switch-controlled, test circuit selection arrangement compelling the sequential performance of different specific tube characteristic tests according to a predetermined sequence.

Other uses and advantages of the invention will become apparent upon reference to the specication and drawings in which,

Figs. lA-lD taken together is an over-all schematic of the multipurpose tube analyzer according tol this invention;

Fig. 2A is a simplified diagram showing the test circuit established when the instrument detailed in Fig. 1 is set for a transconductance test and also exemplifies the dynamic emission tests;

Figs. 5A-3C are simplied circuit diagrams illustrating the principles employed for measuring electrode leakage in accordance with the apparatus of this invention and showing the basic test circuit established when the apparatus of Fig. l is set for leakage testing;

Figs. 4A-4C are explanatory diagrams similar to Figs. 3A3C showing a modied circuit for measuring leakage;

Fig.. 5 shows in simplied form the test circuit established by the mechanism of Figs. lA-lC to obtain and measure control-grid bias;

Fig. 6 is a simplified circuit showing the circuit dened by the mechanism of Figs. lA-lC for measuring rectier characteristics;

Fig. 7 is a simplified circuit showing the apparatus of Figs. lA-lC set up to measure screen grid current and Voltage;

v Fig. 8 shows, in simplified form, the plate readjust mechanism of the present invention;

Fig. 9 is a simpliiied circuit of the mechanism of Figs. lA-lC arranged to measure diode characteristics;

Fig. 10 is a simplified diagrammatic illustration of the portion of the tube tester circuit of Figs. lA-lC showing the mechanism employed for standardizing and calibrating the instrument, and

Figs. 11A-11B illustrate a modified tube electrode selector and leakage test selection circuit which can be employed with the present invention.

The complete circuit of the multipurpose tube analyzer of this invention is detailed in Figs. lA1C, which, taken together, in accordance with the arrangement indicated in Fig. lA form a single circuit diagram. To facilitate the description o-f the construction and operation of the device, however, the various unitary test circuits employed and established by the various circuit positions of the mechanism of Figs. lA-lC are illustrated individually in the various additional figures in simplied diagrammatic form as will be described.

Before proceeding to a detailed description of the invention, it will be well to briefly review certain established characteristics of electron tubes together with the general principles employed by the apparatus of this invention in determining and evaluating such characteristics.

For example, the advantages of an accurate transconductance measurement for determining the condition of new tubes have been recognized. Tube manufacturers measure transconductance for design and quality control and Armed Forces specications enumerate acceptable transconductance limits for allampliier-type*receiving tubes employed for military use. True tube transconductance (Gm) may be deiined as the quotient of a small change in plate current and the small change in controlgrid voltage producing it, under the condition that all other voltages remain unchanged. That is, under dynamic conditions, transconductance is the quotient of the in-phase component of the A.-C. plate current divided by the A..C. signal voltage applied to the control-grid of the tube, under the condition that all other element voltages remain constant,

Conventional nonlaboratory type tube testers fail to indicate a true measure of transcondnctance, because the plate voltages provided do not remain unchanged and because they measure tube transconductance under simulated operating conditions which are entirely different from those conditions which prevail in the actual circuit in which the tube is to be employed. In contrast to the commonly employed grid-shift method, the present invention measures transconductance under conditions which approximate actual operating or service conditions.

In the measurement of leakage, it is common to test various tube types, by providing a plurality of tube sockets adapted to accommodate different types of tubes and connecting each pin of the various tube sockets in common to switch terminals which are used to connect each electrode of the particular tube under test in turn to a particular portion of the test circuit. While such test circuit provides sulicient exibility to enable testing of a wide variety of tubes, the various switch combinations and socket connections will inherently also establish a plurality of circuit leakage paths in addition to those leakage paths which may exist in the tube under test. The apparatus according to the present invention isolates and tests the leakage existing in the tube element iself by simultaneously connecting into the test circuit all electrodes of the tube. In this manner each electrode is successively isolated and the leakage current between such electrode and all other electrodes as a group including the shield is measured under selectively applied leakage test potentials up to 400 volts. ln addition, in order to eiectively measure heater electrode leakage, provision is made to alternately bias the heater element from positive to negative polarity to` compensate for semiconductor characteristics generally exhibited by the insulation in tubes, and for heater electron emission due to space charge eiects.

Other advantages resulting from the apparatus of this invention will` become apparent as the description proceeds.

Figs. lA-l'D is a complete circuit diagram of the tube analyzer comprising the present invention. The details of the power supply employed have been omitted to simplify the disclosure. A voltage-regulated power supply lill including an adjustable D.C. output that can beY varied from -400 volts by means of a control lilla (Fig. 1D) is employed. TerminalA 1 of the power supply 101 provides an adjustable 0-400'volt DC. plate supply Voltage which is regulated by control member 103e; terminal Z'comprises the energy wire for VTVM tube V103 andl is connected to the Zero Adjustment Control R28 as indicated; terminal 3 is the common or ground connection; terminal 4 provides a 105 Volt bias supply and* terminal 5 provides the necessary B-jsupply for the VTVM amplifier 105, signal generator im and screen voltage for the tube under test. As shown in Fig. 1A, the tube analyzer is provided with a plurality oftest sockets only one type of which Xl is shown in Fig. lA. That is, While a standard octal test socket is illustrated, itwill be understood that a suiiicient number of socket types a-re provided to accommodate all types of known` tubes such as seven and nine pin miniatures, octal base tubes, and the less conventional 4 and 5 pin types, for example. Such construction is widely employed in tube tester design and is therefore not further described.

Each of the pins of the test socket Xl is connectedl individually to a respective jack or connector terminaldesignated by the reference numerals l, 2, 3, 4 9 iny Fig.

llA. It is to be understood that a suficient number of such terminals are provided corresponding to the number of pins on the particular test socket employed.

Adjacent to the referred-to jacks 1-9 shown in Fig. lA, there are provided a plurality of additional jacks or connectors labeled H+, H-, P1, P2, K1, K2, G1, G2, GS, GU, D1, and D2. The indicated labeling corresponds to the standard nomenclature generally employed ttor designating the electrodes of a tube. For example, the symbol H designates the heaters, P the plates, K the cathodes, G the grids, and D the elements of a diode.

Provision is made to selectively connect each of the referred-to jacks 1-9 to the above tube element jacks H etc., in the form of patch cord connectors 10. The heater jacks H+ and H are in turn connected to the tapped secondary of a filament transformer T1. By means of a filament-Voltage selector switch S1 any one of the voltages indicated in Fig. 1A can be applied to the heater terminals of the tube under test. The ilexability provided by such arrangement enables the apparatus of this invention to be employed in connection with general analysis work since the jack and patch-cord connection permits auxiliary test equipment and circuits to be integrated into the test circuits of the analyzer.

The general functions ofthe various controls and meters provided to facilitate testing procedures will rst be outlined before proceeding with a detailed description of the operative circuits established during each such test procedure.

Meters Three meters, are employed in the apparatus. of the present inventionto visually indicate the voltages and Qutrents` measured andv applied during each test. Referring. to Fig. 1A, there is shown a. voltmeter M3 for indicating, the; heater voltage selected for application to the tube laments.

The apparatus also includes an extra-sensitive microammeter M1 shown in Fig. 1B for measuring the leakage Current during leakage tests and a voltmeter M2 forming part of. a VTVM. circuit 103 (Fig. 1C).

Switches The switch labeled S1 in Fig. lA, connects thev heater element of a tube under test to any one of a plurality of taps-on the secondary of a iilament transformer T1.

Switch S2, indicated in Fig. 1B is labeled grid current and consists of a tive-position, four-contactor switch. Four of the positions are employed to measure grid currenty of the tube under test, while the mid-position marked normal is employed during other tests.

Switch S3 is the leakage test control switch and is employed to isolate one selected tube element in turn from. all other tube elements whileV tying the latter elements together in a leakage test circuit.

A group of single pole, double-throw switches S4, S5,

S6, and S7 are provided as shown in the center portion of Fig. 1B. These switches are employed in conducting` tests on multisection type tubes for selectively integrating the electrodes in each section of the tube into the test circuit.

Thel switch labeled S8 shown in the lower left-hand portion of Fig. 1A is the Gm range switch and provides meansfor regulating the, range of transconductancevalues measured during a transconductance, or related dynamic emission test as will be later made clear.

A Master Control test switch S9 is provided for establishing the various test circuits employed. Brieily, the following'I functionsare obtained for each position of the .Master Control switch S9: 1

Position 2.: Standard, electrode, leakage test.-Estab lishes leakage test circuit for standard applied leakage test voltage. VTVM meter M2.Y measures the applied leakage test voltage; currentmeter M1 measures the leakage current.

Position 3: Bias voltage test position-Connects VTVM M2 to measure the applied bias voltage; current meter M1 monitors bias supply.

Position 4: Plate voltage adjustment and rectifier test.- Sets up circuit for testing diode rectiliers. In this position the VTVM meter M2 measures applied plate voltage while M1 indicates plate current. 'Ihis position of the switch is also employed to preadjust the plate voltage on tubes having screen grids.

Position 5: Screen voltage adjustment-Connects the tube under test so that the screen grid of tetrodes etc. has a separately applied screen voltage; VTVM meter M2 reads screen voltage and M1 indicates screen current; both plate and screen voltages are applied to the tube under test.

Position 6: Plate voltage readjustment.-Connects Vl VM meter M2 to measure applied plate voltage; connects meter M1 to indicate plate current; separately connects the screen grid of a tube under test to a separate voltage source the amplitude of which has previously been `selectively established in position 5.

Position 7.' Gm Calibrating and standardizing circuit for transcondactance test.-Instrument Calibrating position. In this position the transconductance test circuit is compensated for variations in line voltage or circuit components. VTVM meter M2 is connected to measure the applied signal voltage and the gain of the VTVM; the bias voltage is applied but the plate and screen voltage are not applied to the tube under test.

Position 8.' T ranscondactance test-Establishes the transconductance test circuit. All elements of the tube under test are operatively connected in circuit in this position and a standard 0.1 volt signal is applied to the control grid of the tube. A specially designed high-gain amplifier is also integrated into the VTVM circuit and the meter M2 reads transconductance (Gm) in mhos.

Positions 942: Dynamic emission tests.-Establishes transconductance test circuits for measuring tube transconductance similar to position 8 but applies signal voltages of progressively increasing magnitude to the control grid 0.5, l, 5, and l0 volts respectively; also simultaneously decreases the amplifier gain as the applied signal voltage is increased to maintain a constant Gm ratio. In this manner, the ability of a tube to yield its rated transconductance at diierent signal values is determined.

Position .l-Leakage test position for testing electrode leakage at applied test voltages other than the standard test voltage defined in position 2. The leakage test voltage `can be selectively varied from 0 to 400 volts when S9 is in position 13.

Position 14: Special or detector diode test position.- For testing detector-type diodes. In this position the VTVM M2 is automatically connected to indicate in a .20-volt range and M1 is set to a 3 ma. range.` Moreover, the plate voltage is applied through a regulated source in this position to limit the amount of current to 2.5 ma. in order to prevent damage to the diode under test.

Switch Si() shown in the upper left-hand portion of Fig. lC is a multicircuit switch and is employed as the line-range selector for current meter M1.

The switch labeled S11 adjacent S10 in Fig. 1C is a single-pole, double-throw switch which cooperates with range selector switch S to establish the course range of adjustment for meter Ml.

The potentiometer labeled R25 adjacent S11 in Fig. 1C is the Gm Calibrator and is used for standardizing the instrument when conducting the referred-to transconductance tests. Switch S12 is the Zero Set switch used to ground the control grids of tube V103 While the Zero Adjust control R28 is adjusted for a zero reading of M2.

The switch S13 in Fig. 1D is a plate-voltage rangeselection switch which sets the VTVM to the proper range corresponding to the amplitude of the plate volt- E age applied to a tube under test by the regulated pwe supply.

The switch S14 is a screen-voltage range-selector switch and is similarly employed to select the VTVM range to indicate the amplitude of the applied screen voltage.

The switch S15 is a bias-voltage selector switch and provides a means for obtaining an adjustable bias voltage.

Leakage test circuit (F gs. 3 and 4) lt is feasible to first describe the structure features of the apparatus of the present invention which coopcrate to provide the leakage test circuit. Many of the circuit elements employed in the leakage test also cooperate when properly oriented with other circuit components to provide diEerent tube characteristic tests as will become apparent in subsequent portions of the present disclosure.

Many of the leakage and short test circuits now in use fail to check all tube elements simultaneously and therefore do not accomplish a complete leakage or short test. In addition, numerous controls have to be operated in order to check the leakage of each tube electrode. Moreover, as far as is known, none of these circuits take into account the electron emission of the heater of indirectly heated, cathode-type tubes.

The insulation test voltage of the apparatus shown in Fig. l can be adjusted to any desired Value between 0 and 4G() volts in accordance with the principles of the present invention. The meter M2 shown in Fig. 1B is used to indicate the leakage-test voltage applied and a sensitive microammeter M1 is employed to measure the leakage current. The leakage test circuit employed with the present invention is designed so that nine different tube electrodes, the maximum number having separate external connections, can be isolated with respect to all remaining tube elements and individually tested by merely rotating the leakage test switch S3 through its 14 adjustable positions.

When the leakage test switch S3 is in position 2, the heater of the tube under test is isolated and connected to the positive side of the insulation-test voltage supply, and all remaining elements of the tube under test are tied together and connected to the negative side of such voltage source. Since such biasing arrangement is of opposite polarity to that required to produce electron emission in an actual circuit, the current indicated by meter M1 is due entirely to the resistance of the insulation between the heater and all other elements.

Similarly, with the leakage test switch S3 in position 3, the heater will be isolated and connected to the negative side of the leakage test voltage source, and all remaining elements are connected in common to the positive terminal of such source. Since the polarity of the test voltage is now such as to induce electron emission, the current indicated by M1 is due both to the electron emission of the heater and to the leakage current between such heater element and all other tube elements. When the leakage resistance of tubes is measured with the heater at a negative potential with respect to the other elements, tubes which have been found to introduce hum Will invariably show a much higher leakage current than tubes which are not defective in such respect. In this respect, the present invention provides a critical qualitative basis for evaluating tubes under actual service conditions.

Moreover, the leakage test circuit employed in the present invention provides for the measurement of the insulation resistance of filament type or directly heated cathode tubes.

The multisection, multiposition leakage test switch S3 indicated in Figs. 1A and 1B has a suiicient number of positions as shown to accommodate all possible electrode combinations. In connection with leakageftest switch' S3r..aswell asY other-multisection switches to be described, each section or deck is labeled from A-N. The contaeterterrninal of;V the` switch, is referenced with numeral i while the remaining switch-terminals are consecutively numbered. The l position of the leakage test switch.

is the zero or inactive position and when in such position, alli of the jacks except the twoA heater jacks` H-, H+ of.v the,` patch c ord system; are disconnected from the test circuit to enable the various test circuits to be set up. ln this position the electrodes of the tube under test are isolated from the test circuits. Tracing the leads froml the jacks H1 to D respectively, it will be apparent that each of thev jack terminals are connected respectively to each off the leakage test switch contactors according tothe following pattern:

JackY designation-,z Contactor or deck It will be apparent therefore, that each pin of the test socket exempliiied by X1 is connected to one of the contactors or wiper arms of a respective switch section. At this point in the description the simpliiied leakage test circuits illustrated in Figs. 3 and 4 of the drawings can be considered.

Figs. 3A, 3B, and 3C clearly illustrate the principles of eecting leakage tests in accordance with the apparatus of this invention. Fig. 3A shows a tube VX under test in which the heater is isolated with respect to all of the remaining tube electrodes, and is connected to the positive siderof a leakage test voltage source through current indicator Ml and resistor R27. Fig. 3B shows the heater connected to the. negative side of the leakage test voltage source and isolated. with respect to all the remaining electrodes of a twin-triode type tube. Fig. 3C shows the testconnections for a twin-triode with one of theV plates isolated with respect to all of the remaining tube electrodes and connected to the negative side of the leakage test voltage source. Figs. lA-4C are leakage test circuitsv similar to Figs. 3A-3C but employ a slightly modified test circuit arrangement. it will be noted in the modiiicationsrof Figs. lA-4C, the meter M is included in the grounded side of the test circuit permitting Iuse of .lower qualit-y and lessexpensive components in the leakage test circuit.

The leakage test switch S3 described in connection with Figs. lA and 1B provides the4 necessary means for selectively orienting the electrodes under test in the manner exemplified in Figs. 3A-3C. For example, when leakage test switch S3 is set to test position 2, the following circuit connections will prevail: Frorn` (G1) to A2 to B2. to (G2) to S6 to D2 to (K1) to E2 to (K2) to F2 to (D1) to G2,to (D2) tov H2 to (GS) to I2 to (GU) to K2 to (P1) to L2A to (P2). The symbols indicated in parentheses. correspond to the referred-to jack connections or tube electrode designations while the remaining designations refer to the particular switch section contacts of leakage test switch S3 concerned. By grouping together the designations indicated in parentheses, it willv be` apparent that tube electrodes G1, G2, K1, K2, D1, G2, D2, GS, GU, P31., andA P2 are tied together and are further connectedV to ground or B-..

The leakage test controll switch S3 can be set to each ottwelve test positionsA inl cach of which dilerentones; of

Position of test n Arrangement and polarity offtube elements: Switchs?,

' Heater or filament positive, all other elements negative.

-vHeater or filament negative, all other elements positive.

Plate No. 1 negative, all other elements positive.

Plate No. 2 negative, all other elements positive.

Heater and cathode No. 1l positive, all othery elements negative.A

Heater andv cathode No. 2 positive, all other elements negative.

l Control gri'd- No. 1 negative, all other elements-positive. Control grid No. 2 negative, all other elements positive. Screen grid negative, all:other elements positive: l Suppressor grid negative, all other elements positive.

Diode 1 negative, all other elements positive.

Diode Zinegative, all other elements positive.

In conducting leakage tests, the; master control S9 (see-Fig. 1B) is setto position 2 as will be describedy for; testing leakage at ay standard` voltage, or to position l-3 if the rating of the tube under test is such` that a voltage higher or lower than the standard test voltage of approximately 9.0 volts is required.

Furthermore, the grid curren test switch S2 is set toA normal position during all leakage tests. With switch S2 setto nor-mal position, the heater electrodes of theY tube under testwill be included in the leakage test circuit but isolated from thel remaining electrodes and a test circuit will be established for impressing a selected best voltage and' for indicating any leakage current in the manner diagrammatically illustrated in Fig. 3.

Referring to Figs. lA-l-D the heater electrode H+ is shown connectedto one of the selected positive taps on transformer-T1l while the H- terminal of the heater eiement is connected' from the Zero voltage terminal, through thecontactor (terminal il) of deck C of leakage test control switch S3 (Fig, 1B) through contact 2 ofdeck C to the contactor (terminal il) of deck M; A connection is-thereby.- established from the contactor'of deck M to section-Bfof gridcurrent switch S2. When S2 is in a normal test position', contactor B` of S2 will establishav connection-through resistors Rlllti, RM1 (shown iii the middlel of Fig. 1) and to one terminal ofv an extrasensitive microainm-eter Ml (Fig. 1B). The circuit then continues from' the other terminal-of Mi to contactor A' of S2. Since S2 is in a-normal position durin'g'a leakage test, a-circuit is established to the contactor of deck N. of leakage test switch S3', through terminals C2 to C8y of-sueh deck, and thence to the contactor of deck C ofl master control switch S9. Master control-switch S9 being set to the referred-to test position 2, shown in the drawings, the circuit is continued through the contactor of deck D of S9 to resistor R27 shown in the upper righthand portion of Fig. 1D. The opposite terminal of R27 is connected to the movable contact of potentiometer Rltl; The potentiometer R106 is initially adjusted to`- provide a leakage-test voltage or" volts. Decks B and' A of S9 connect RlGS (Fig. 1C) to the junction of R27 and the movable contact or" Rlii. The remaining electrodes of the tube under test, for example, P1, KE, and H in the case of a triodey are connected to the contactor of the respective switch banks SBK, SSD, andf 53A. Assuming S3 to be in position 2, all such electrodes are accordingly tied together by conductor 162 and connected to the negative side of the power supply. It will be apparent from such circuit description, that a test circuit equivalent to that illustrated in Fig. 3A is established, with the heater electrode isolated from the other electrodes consideredas a unit, and connected to the positive side of a leakage-test potential source and including a leakagecurrent indicator Mizin series with the heater electrode under test.

In. order; to. connect the heater negatively according to the test circuit schematically-indicated in Fig. 3B, provision isymade` for connecting therernaining electrodesl :which have been tied together as described, to a positive source and for connecting the heater electrode to ground, or negatively with respect to the remaining electrodes.

Specifically, such circuit change is easily eected in accordance with the apparatus of the present invention by advancing leakage test switch S3 to position 3 as indicated in Table 2. In such position of S3, the polarity of the voltages applied respectively to the grouped electrodes and to the heater are reversed so that the grouped electrodes are now connected to the positive side of the leakage-test voltage source through a circuit including the meter M1 and resistor R27 While the heater elements are now returned to ground or to a negative source which is negative with respect to the positive voltage source. The resulting circuit is represented in Fig. 3B which diagrammatically illustrates the leakage test conditions when the heater element is isolated and negative with respect to the remaining elements.

In order to comply with the requirements of the patent statutes, the specific circuitry established during the various leakage tests is described in greater detail below. The principles underlying the test circuit however, are fully illustrated in the digest diagrams of Figs. 3 and 4 and explained above.

It will be noted that when the master control switch S9 is in position 2, decks A and B of S9 connect R103 (Fig. 1C) to the junction of R27 (Fig. 1D) and the movable contact of R106 (Fig. 1C), thereby connecting the positive VTVM voltage divider circuit consisting of R103, R101 (Fig. 1C), R34, R33, R32, R31, R30, and R29 (Fig. 1D) connected in series across the leakage-test voltage source 101 shown in the lower right-hand portion of Fig. 1D. Decks C and D of S9 connect R27 in series with a movable Contact on resistor R106 and contacts 2 to 13 of deck N of the referred-to leakage test switch S3. Deck G of the master control switch S9 connects the control grid of the VTVM tube V103 (Fig. 1C) to the juncture of R31 and R32 (Fig. 1D), thereby establishing a 10U-volt range for the VTVM meter M2 employed to register or indicate the applied leakage test voltage.

1n addition, when the leakage test switch S3 is` in any position from 2 to 13 as enumerated in Table Il, deck N of such switch connects the negative end of R27 to the positive terminal of the sensitive microammeter M1 used to measure the leakage current, and deck M of S3 connects the negative end of R110 to the particular tube electrode which has been isolated for the leakage test and connected by decks A to L of S3 to contacts 2 to 13 of deck M.

Since resistors R110 and R111 (Fig. 1C) are connected in series to the negative terminal of microarnrneter M1 the latter is connected in series with the established leakage test circuit and will indicate the leakage current in na. The total series resistance provided by the described resistors comprising the leakage test circuit is indicated in both Fig. 3 and in the modification of Fig. 4, and is such that any shorted elements in the tube under test or any having very low leakage resistances will produce a leakage current of 50 tra. and a full-size deilection of the microammeter M1.

The referred-to VT VM voltage divider (R103 etc.) is connected across the leakage test voltage supply and the meter M2 does not therefore measure the voltage applied to the tube elements. However, since a regulated voltage supply 101 is employed, the need for adjusting the Zero set control R28 is immediately made apparent if the reading of M2 is not exactly 90 volts.

Setting the master control switch S9 to any position other than 2 or 13 removes the leakage test voltage from the elements of the tube under test. The voltages required for other tests can be applied only when S3 is in position 14. In position 2, a standard test voltage ot 90 volts is applied. To obtain other leakage test voltages either less than or greater than the 90-volt standard 10 voltage, S9 is advanced to position 13 which causs the Various decks A-M of switch S9 to connect the leakagetest circuit to the plate voltage control S13.

Testing electrode leakage at test voltages other tha standard test voltage Provision is also included in the apparatus of the present invention to measure electrode-leakage currents at test potentials which can be selectively varied through a range extending from z'ero to 400l volts or any larger potential depending on the particular type of power supply 101 employed. To make leakage measurements at other than the standard test potential of volts established when master control switch S9 is in position 2, the latter is advanced to position 13. In such position, decks A and B of S9 connect the resistor R103 to R26 placing R26 in series with the positive voltage divider across the variable D.C. terminal of the power supply as shown in Fig. 1D. Decks C and D of S9 connect the junction between resistors R20 and R23 to the terminal between resistors R103 and R26. Deck E of S9 connects the junction between resistors R24 and R110 to contact 2 to 13 of deck M of the leakage test switch S3. Deck F of S9 grounds some circuits not used in position 13 of S9. Deck G of S9 connects the first control grid of VTVM amplifier tube V103 to the movable contactor of plate voltage range selector switch S13. Deck H of S9 grounds the second control grid of V103. Decks l, K, and L of S9 make no connections in position 13. Decks M and N connect contacts 2-13 of S9 to Contact 14 of deck M of the leakage test switch S3.

The test potential applied to the leakage test circuit established by master control S9 in position 13 is selectively adjustable by means of the plate voltage range selector switch S13 and the output voltage adjusting means 101e (Fig. 1D) provided in the power supply. The applied test potential is indicated on the VTVM meter MZ (Fig. 1B). Since resistors R23 and R24 (Fig. 1C) are connected in series with the leakage test circuit and form a shunt resistance of 200 ohms, the current ranges established for the current indicating meter M1 are 0.5, 1.5, 5, and 15 ma.

Upon compietion of the leakage test, the leakage test switch S3 must necessarily be advanced to position 14 in order to establish the necesasry connections required for the other test circuits. In this manner the switch S3 in effect compels all leakage tests to be performed in sequence, and further insures isolation of the leakage test circuits from the ensuing test circuits.

1t Iwill be noted from the circuit diagram of Figs. 1A- lD, that master control switch S9 does not control the functions of the grid current switch S2, and therefore the grid current can be measured during any and all ensuing steps of the test procedure following the positioning of S3 to position 14.

As previously noted, when the grid current switch S2 shown in the upper portion of Fig. 1B is in normal position, contacter A of such switch connects the positive terminal of M1 to the contactor of deck N in switch S3, and contactor B of S2 connects resistor R110 (see Fig. 1C) to the contacter of deck M in switch S3. Since resistors R and R111 are connected in series to the negative terminal of M1, the negative side of such meter is connected to deck M of S3.

When the leakage test switch S3 is advanced to the position 14 indicated in Fig. 1, each of the electrodes of the tube under test which, as described, are connected to the respective contactors (terminal 1) in banks A-L of switch S3, will be isolated from the previously established leakage-test circuits and will be connected according to the following arrangement:

Grid No. l electrode (G1) to S3A to G1 of S5;

Grid No. 2 electrode (G2) to S3B to G2 of SS;

Heater electrode (H-) to 83C to S6 (ground); Cathode No. 1 electrode (K1) to S3D to K1 of S67; v

Cathode No. 2 electrode (K2) to SSE to K2 of S6; Diode No. 1 electrode (D1) toS3F to D1 of S4; Diode No. 2 electrode (D2) to S3G to D2 of S4; Screenv grid electrode (GS) to S31- to contactor of deck .l of S9; Suppressor grid electrode (GU) to S3] to S6 and ground; Plate No. 1 electrode (P1) toSSK to 11l of S7; Plate No. 2 electrode (P2) to S3L to P2 of S7.

Itnwill be. apparent, therefore, that suitable conditions have been established so that. master switch S9 can now assume command and orient. the various tube elements into respective test circuit` patterns established by the master switch S9 as it is set into each of the respective operative positions 3-12 and 14. Each of the test circuits established by such positioning of the master switch S9 willl now be described in order.

Bias-voltage circuit switch S9 in position 3 (Fig. 5)

Preliminary to any transconductance measurements, the grid bias of the tube under test must be accurately established. Inrthe present invention the necessary circuit arrangement for adjustably presetting the grid bias is btained when the master. switch S9 is advanced to position 3. Inthis position, the VTVM 103 (Fig. 1C) is connected to indicate bias voltages. It will be apparent, by tracing the circuit connections established in positions 3 of S9 that decks A and B- of S9 connect R104 (Fig. 1C) to the movable contacter of the bias voltage control R59. shown at the lower right in Fig. 1D, thereby, connecting the negative portion of the VTVM voltage divider (R104. etc.) across the voltage source 101.

Fig. 5 is a simplified circuit diagram showing the connections and circuitry established with S9 in position 3. Since all components shown in Figs. lA-lD are identiiied by. like reference numerals in Fig. 5, it will only be necessary to follow the relatively simplified circuitry shownin.

Fig. 5 for a description ofthe bias voltage circuit. Decks C and D of S9 connect the junction between R20 and R23 to ground. Deck 89E connects the junction of R24.. Deck of. S9:

and R110to the positive end of R60. grounds all circuits not used when S9 is in position 3. In addition, deck G of S9 grounds the control grid 1 of the VTVM tube V103 and deck H connects the second control grid to the movable contactor of section A of the bias voltage range selector switch S (Fig. 1D). In position 3, decks l, K, L, M, and N of S9 make no connection.

Section A of the bias voltage range selector switch S15 controls the connection or the second control grid of VTVM tube V103 to any one of the junction points of a negative voltage divider consisting of resistors R104, R102 (Fig. 1C), R57, R56, and R55 (Fig. 1D). Sections B- and C of S15 control the voltage applied. across a bias voltage control R59, the adjustable member of whichis connected through a choke L1 (Fig. 1B) to the control grid of the tube under test. That is, the range selector scale for S15 is calibrated to read 10, 40, and 100 volts as` indicated both in Figs. l and 5. When S15 isset to a lll-volt position, section A connects the second control grid of VTVM tube V103 to the junction between R102 and R57, thusV providing a l0-volt range for voltmeter M2. Sectionsv B and C of S15- connect the bias voltage control R59 into the resistance network, as shown in Fig. 5, consisting of resistors R50 to R54 and R58, so that the voltage across bias voltage control R59. has a range between 0 and `--11 volts. When S15 is advanced to a 40-volt position, section A connects. the second control grid of V103 to the junction between resistors R57 and R56 in which case 40 volts will produce afull-Scale deection of the voltmcter M2 and sectionsY B and C connect bias control R59 so that its range of adjustability is between -9 and -42 volts. ln the 10Q-volt positionV of S15, section A connects the control grid of' V103 to the junction between resistors R56 and R55, a position in which 100 volts will produce a full-scale deflection ofethe voltmeter M2, While sections B and C connectr R59: so that its voltage range extends from -37 to -105 volts. The bias voltage is held constantby the regulated'power supply 101 employed. It is obvious that if even liner control of the bias voltages is desirable, S15 can be replaced by a 3-pole switch that has the additional positions required to provide any other voltage range ratios desired.

The resistance of R60 and that ofthe shunt and seriesl resistors of the microamrneter M1'- are such that, if no= abnormal condition exists, M1 will read full-scale, whenv the current indicator range selector switch S10 is in itsA normal position and an associated single-pole, doublethrowtoggle switch S11 (course control) is set to a 5- and SO-ma. range position. With the above-described'. arrangement of voltage and current indicators and controls, a rapid check of the entire bias and the entire current measuring circuits is obtained. For current ranges of-Y 5, l5, 50, and ma., the 20-ohm resistor R24y (Fig.

1C) forms the shunt. resistance for M1. Resistors R20,

R21, R22, R23, R110, and R111 (Fig. 1C) formA the series resistance which connects the meter M1 in parallel with resistor R24. When the current range selector switch S10 is in its normal position and range selector S11 is in a 15C-ma. position, the total series resistance, including the resistance of M1 is 59,980 ohms. selector S11 to the 50-ma. position shorts out R22 and reduces the series resistance to 19,980-ohms. range selector switch S10-for meter M1 in the 15-ma. position shorts out R21 and -reduces the series resistance to 5,980 ohms. Advancing range selector S10 to the 5-ma. position reduces thel series resistance to 1,980 ohms. ln order to protect the current meter M1, range selectorV switch S10 is preferably of the type which includes a spring-return mechanism so that when it is in its normal position, the current range of M1 is either 50 or 150 ma. depending upon the setting of range selector S11.

For current ranges of 0.5, 1.5, 5, and 15 ma., the 180- ohm resistor R23 is connected in series with R24 to form a shunt resistance of 200 ohms. Under such condition, the series resistance in the 15-ma. range is 59,800 ohms; in the S-ma. range, 19,800 ohms; in the 1.5-ma. range,

5,800 ohms; in the 0.5-ma. range, 1,800 ohms. Resistor- R111 is adjusted so that the series resistance of M1, R110 and R111 is exactly 1,800 ohms.

In the above-described manner, when the master switch S9 is in position 3, any selected bias voltage up to 100v volts is obtainable for application to the grid of the tubel under test. As each bias range is selected by adjustmenty of bias range selector switch S15, the VTVM circuit is automatically arranged to give a full-scale meter deection on the meter MZ. The bias voltage circuit is employed to adjust the instrument to provide the correct tube bias for the particular tube being tested subsequent to performance of a tube transconductance measurement. However, since position 4 of master switch S9 provides a diode-rectifier test circuit, the construction and mode of operation of such rectifier test circuit will be described before proceeding to a description of the transconductance test.

Diode rectification test and plate readjust circuit-Switch S9 in position 4 When the master control S9 is advanced to position 4 decks A and B connect resistor R103 of the VTVM voltage divider to the positive terminal of the variable regulated power supply 101. The circuitry established with S9 in position 4 in the circuit diagram of Fig. 1 is repre sented in simplified form in Fig. 6. The same reference numerals appearing in Figs. lA-lD are employed t0 designate like parts in Fig. 6. In order to further simplify the disclosure, the ultimate connections established by 1 but not the switch terminals of master switch S9 arev in'- dicatedin Fig. 6.

Accordingly, decks C and Dof the switch S9 shown in Setting the rangeA Holding the- Figs. lA- will establish a connection between the junction of resistors R23 yand R24 to the positive terminal 1 (Fig. 1D) of the power supply. Deck E of S9 connects the junction of R24 and R110 to the contactor 4 of deck K which establishes a circuit to the contactor of a singlepole, double-throw toggle switch S7, designated as plate switch in Figs. 1B and 6. Deck F of S9 in Fig. l serves to ground some of the circuits which are not used when S9 is in position 4. Deck G connects the first control grid of the VTVM tube V103 to the movable contact of a plate voltage range selector switch, S13 and deck H grounds control grid 2 of V103. Decks l, L, M, and N make no connections when S9 is in position 4. The resulting circuit in simplified form is shown in Fig. 6.

` 'The referred-to plate voltage range selector switch S13 controls the connection of control grid 1 of VTVM tube V103 to the consecutive junction points between resistors R29 to R34 `and R101 which provide a full-scale deflection for voltmeter M2 corresponding to 400, 200, 100, 40, 20, and 10-volt ranges, respectively. Actual control over the plate voltage applied to the tube under test is obtained by by the adjustable member 101a on the regulated power supply which is of a conventional type that can be varied between O and 400 volts under a load of up to 225 ma. The control member 101a is operatively connected to the plate voltage range selector switch S13 as indicated by the dotted line connection in Fig. 1D. The range selector S13 therefore functions to control the voltage range of the applied plate voltage and to automatically select a voltage range for VTVM 103 that will produce a full- Scale deflection of the VTVM meter M2.

4 In position 4, decks C, D and E of master control S9l connect the current meter M1 into the plate circuit of the tube under test as indicated in Fig, 6 so that the ZO-ohm resistor R24 forms the total shunt resistance. Therefore, the current ranges established for meter M1 are 5, 15, 50 and 150 ma. lt will be apparent from the above description that position 4 of master control switch S9 establishes a rectifier test circuit capable of testing rectiiiers in accordance with manufacturers specifications.

Position of S9 screen voltage adjustment When the master control S9 is set to position 5, decks A and B connect resistor R103 to the movable contactor of a screen voltage control R42 thereby connecting the positive scale of the VTVM voltage divider (R29, R30 etc., see Fig. 7) across the applied screen grid voltage. Fig. 7 is a simplified diagram of the screen grid circuit established when master control switch S9 is in position 5. Decks C and D of S9 (Fig. l) will establish the circuit diagrammatically shown in Fig. 7 in which the junction of resistors R23 and R24 are connected to the slider of the adjustable screen grid Voltage control R42. Deck E of S9 will connect the junction of resistors R24 and R110 to contactor 5l of deck J which in turn establishes a circuit to contactor 14 of deck H of the previously described leakage test switch S3. Deck F of S9 grounds some of the circuits not used in position 5 of S9. Deck G connects control grid 1 of VTVM tube V103 to the movable contactor of deck A of a screen voltage range selector switch S14 shown in both Figs. 1B and 7. Deck H grounds control grid 2 of V103. Deck K of S9 connects the B-joutput terminal of power supply 101 to the movable contact of plate switch S7. Decks L, M, and N make no connections when S9 is in position 5 When the screen voltage range selector switch S14 is in position Eg2=Eb (see Fig. 1D), deck A connects control grid 1 of V103 to tne movable contactor of plate voltage range selector switch S13, deck B disconnects the low-voltage terminal of screen voltage control R42 from the resistance network consisting of R35 to R41, and deck C disconnects the high-voltage terminal of R42 from the resistance network R43 to R49 and connects it to the adjustable regulated power supply 101. In this position, the adjustable regulated power supply 101 14 simultaneously controls both plate and sr'een voltages and the plate voltage range selector S13 now controls the voltage range of the Vl VM meter M2. In such position of the controls, adjustment of the screen voltage when the screen voltage of the tube under test is equal to the plate voltage is unnecessary.

In the remaining l() positions (labeled l0, 20, 40, L, lOOH, ZOOL, 200H, 400M, and 4001-1 in Fig. 1D) of the screen voltage selector switch S14, deck A connects control grid 1 of V103 to that junction of the VTVM voltage divider (R29, R30 etc., Fig. 7) which provides the most appropriate range for meter M2 to cover the voltage range selected by decks B and C for application to the screen voltage control R42. The energizing power for the screen of the tube under test is obtained from the power supply 101 which also supplies the bias voltage and all operating voltages for tubes V101 to V106.

Since decks C, D, and E of S9 connect the current meter M1 into the screen circuit so that the 20-ohm resistor R24 formsy the total shunt resistance, the ranges of M1 for measuring screen current are 5, l5, 50, and ma. The above-described circuit provides an extremely smooth screen voltage adjustment and the eect of readjusting the plate voltage when master control S9 is in position 6, changes the screen voltage so slightly that it seldom is necessary to set S9 back to position 5 to check the screen voltage.

Position 6 of master Control .S9-plate voltage readjustment When the master control switch S9 is in position 6, deck l connects the movable contactor of screen voltage control R42 directly to contact 14 of deck H of the leakage test switch S3 and the function of all of the other decks is the same as that previously described in connection with position 4 of S9 (plate voltage adjustment position). Position 6 establishes the conditions required to check and, if necessary, readjust the plate voltage and to measure the plate current after the screen voltage has been applied.

The values of the required plate and screen voltages having been established in this manner and individually applied to the plate andl screen electrodes of the tube under test, the master switch S9 can now be advanced to position 8 in which it establishes a transconductance test circuit now to be described. The transconductance test circuit employs the above-described circuits for separately energizing the plate and screen electrodes of the tube under test. y

However, to facilitate accurate performance of the transconductance test, the instrument according to the present invention incorporates a special circuit for calibrating and standardizing the mutual conductance test circuit established when master switch S9 is advanced to such position 8. The connections for such Calibrating and standardizing circuit are made when the master switch is set to position 7 prior to conducting the transconductance and related dynamic emission tests. The circuits employed for transconductance measurements and for calibration and standardization thereof are essentially the same except that provision is made for adjusting the ratio between the measured amplitude of the signal applied to the grid of the tube under test and the A.C. plate signal derived therefrom to a predetermined value. Before describing the specific construction and operation of the transconductance circuit, the construction land operation of the Calibrating and standardizing network will first be referred to.

Calibrating and standardizing the mutual conductance circuit position 7 of master switch S9 The portion of the circuit shown in Figs. lA-lD ernployed for standardization is illustrated in simplified diagrammatic ,form in Fig. 10. Such circuitl isestablished 

